[MrX]

Not that different really:

The current 24km of Luas cost about €800m — or €33m per km

Although Luas largely ran over the Harcourt line on the green route
and over relatively cheap land into Talaght.

The paris line's right through the city itself.

(Although on public roads too)

I think Luas has been a general PR success story though and might help future line development.
People have seen their house prices rocket along the line and I don't think you'll see as many objectors as you saw with the initial project. People see the benefits and have largely forgotten about the disruption during construction phases.